jeff8407 wrote:Bubble wrap is not better. However, most slabs lose their heat from the edges ,and if you use bubble wrap under the footings and up the sides of the slab the heat will be forced up instead of out. Insulating the sides of the slab is of the utmost importance either way you go. Remember, heat like water, and money in politics, will find the path of least resistance and go where it is easiest to "flow." Insulation just directs the "flow".

The idea behind the bubble wrap is to force the heat up or down instead of out the sides. Even if heat is transferred under the building the idea is that the soil will act as a huge heatsink and eventually it will come up into the building--in some areas it can be typical to leave the center section of the slab uninsulated--I do not know why, but have a few ideas.

Personally, I would insulate the floor and sides with foam and footings with either(bubble wrap is easier to lay into the footings and pour concrete into). I think using the foam you have is a no brainer.

There is no such thing as a “dead” air space as far as heat transfer is concerned, even in the case of a perfectly airtight compartment such as a thermos bottle. Convection currents are inevitable with differences in temperature between surfaces, if air or some other gas is present inside. Since air has some density, there will be some heat transfer by conduction if any surface of a so-called “dead” air space is heated. Finally, radiation, which accounts for 50% to 80% of all heat transfer, will pass through air (or a vacuum) with ease, just as radiation travels the many million miles that separate the earth from the sun.

Aluminum foil, with its reflective surface, can block the flow of radiation. Some foils have higher absorption and emissivity qualities than others. The variations run from 2% to 72%, a differential of over 2000%. Most aluminum insulation has only a 5% absorption and emissivity ratio. It is impervious to water vapor and convection currents, and reflects 95% of all radiant energy which strikes its air-bound surfaces.
HEAT LOSS THROUGH FLOORS

Heat is lost through floors primarily by radiation (up to 93%). When ALUMINUM insulation is installed in the ground floors and crawl spaces of cold buildings, it prevents the heat rays from penetrating down, reflecting the heat back into the building and warming the floor surfaces. Since aluminum is non-permeable, it is unaffected by ground vapors.

Heat is lost through floors primarily by radiation (up to 93%). When ALUMINUM insulation is installed in the ground floors and crawl spaces of cold buildings, it prevents the heat rays from penetrating down, reflecting the heat back into the building and warming the floor surfaces. Since aluminum is non-permeable, it is unaffected by ground vapors.

I've got a 26x50ft shop with heated floor, problem free for 16 years now. I heat it with one 40gallon propane hot water heater and also have a wood boiler when I want to burn wood. One thermostat, one circulation pump, and one expansion tank. Simple setup. The biggest things when doing the floor is get a base of sand down and compact it well, put a good moisture barrier down-plastic, put insulation down-I used the thin aluminum foil type in the shop and I used 2" pink foam sheet insulation in my house basement-both work fine, put insulation around the perimeter of the slab as well, lay in your rerod or mesh sheets and zip tie the tubing in place, keep the tubing 2 feet from the outside perimeter of the slab, pour the concrete and pull up on the rerod or mesh so you center the tube in the slab. It was -28F a few days ago here and my shop stays 65F all winter long. There's a few different types of tubing designed for this, I used the rigid plastic coated aluminum type in the shop and the stuff I put in the house looked like black fuel line but it has a plastic inner liner. The rigid stuff was easier to work with-holds the bends well when you're laying out the grid.

Bubble wrap vs foam board for under slab....
Ask 10 people and you will get 12 different answers. My question is... who thinks bubble wrap has any insulation value when no air barrier on either side?
It is used in ceilings and walls on pole barns.
It is much cheaper, though.
I have looked... will someone find an R value on bubble wrap between 2 solids (dirt and cocnrete in this case)?
The R value for foam board is what it is. Not subject to conditions...
I might be fucking up... I have talked to tons of folks...
I will report back in 5 to 15 years and let you know how it holds up. HA
My 4500' of pex and manifolds showed up Thursday. I guess time to stop drinking and start working again.
Wags

wagspe208 wrote:Bubble wrap vs foam board for under slab....
Ask 10 people and you will get 12 different answers. My question is... who thinks bubble wrap has any insulation value when no air barrier on either side?

The bubble wrap I use is 4.2 with no air and 6 with.
The question should be is how much re-bar do you want to use when using foam?

our last house we expanded the garage used in floor heat with a boiler 24x20 worked great low cost.moved built 5000 ft shop.2000 ft heated with in floor heat.so called expert told me a boiler was over kill,WRONG told me to use 50 gal water heater.its on 24/7 3-400 per month thats at 50 degrees.screw that leave it at 40 and put on a modine style heater on ceiling turn it on when im in there works great and cut the bill by at least half. very well insulated.in floor in concrete is not ment to turn on and off. takes forever to heat the slab.

jake197000 wrote:our last house we expanded the garage used in floor heat with a boiler 24x20 worked great low cost.moved built 5000 ft shop.2000 ft heated with in floor heat.so called expert told me a boiler was over kill,WRONG told me to use 50 gal water heater.its on 24/7 3-400 per month thats at 50 degrees.screw that leave it at 40 and put on a modine style heater on ceiling turn it on when im in there works great and cut the bill by at least half. very well insulated.in floor in concrete is not ment to turn on and off. takes forever to heat the slab.

That is the reason my machinist friend ended up calling me because his bill was outrageous using the 2 50 gallon water heaters. 1 for the shop and 1 for the house.... I put 2 on demand water heaters with a heat ex-changer so the domestic water is separate and cut his bill in halve.
He could have saved more if he had laid the tubing better other than the 12" center and 2 feet from the walls But oh well it's done.

Mine is Vapor barrier then 2" foam then rebar with pex tubing in the middle of 5" of cement,30' x30' with 4 seperate loops( you do not want 1 continous run). thermostate controlled ,wood fired boiler, does the shop, basement and house,keep the shop and basement at 65 degrees all winter. Great when you have to lie on the floor to wok on the car.

thphtm wrote:Mine is Vapor barrier then 2" foam then rebar with pex tubing in the middle of 5" of cement,30' x30' with 4 seperate loops( you do not want 1 continous run). thermostate controlled ,wood fired boiler, does the shop, basement and house,keep the shop and basement at 65 degrees all winter. Great when you have to lie on the floor to wok on the car.

It all has to do with the Pump used. 300' max is the most I will run on 1 pump.

I find the biggest pain with in-floor heating is it becomes difficult/risky to drill holes in the floor to mount machinery. It's also not good for spaces that aren't constantly heated as it has a slow response time.